Place the ¾ cup walnut halves toasted and roughly chopped halves in a dry Skillet over medium heat. Toast, stirring frequently, for 3–5 minutes until fragrant and lightly golden. Remove from heat, let cool slightly, then roughly chop.

In a small Mixing Bowl, whisk together the ½ cup mayonnaise, 3 tbsp plain Greek yogurt or sour cream, 1 tbsp lemon juice freshly squeezed, 2 large crisp apples such as Honeycrisp or Fuji, cored and diced into ½-inch pieces, ¼ tsp fine sea salt, and 1 pinch freshly ground black pepper until smooth and well combined. Taste and adjust seasoning — add a little more 1 tbsp lemon juice freshly squeezed for brightness or 2 large crisp apples such as Honeycrisp or Fuji, cored and diced into ½-inch pieces for sweetness.

Core and dice the 2 large crisp apples such as Honeycrisp or Fuji, cored and diced into ½-inch pieces into ½-inch pieces (no need to peel). Thinly slice the 3 stalks celery thinly sliced and halve the 1 cup red seedless grapes halved. Add the 2 large crisp apples such as Honeycrisp or Fuji, cored and diced into ½-inch pieces, 3 stalks celery thinly sliced, 1 cup red seedless grapes halved, and toasted ¾ cup walnut halves toasted and roughly chopped to a large Mixing Bowl.

Pour the dressing over the salad ingredients and gently fold everything together until evenly coated. If serving on 4 cups romaine lettuce chopped, for serving, arrange chopped 4 cups romaine lettuce chopped, for serving on a platter or individual plates and spoon the Waldorf salad on top. Serve immediately or refrigerate for up to 30 minutes before serving for the flavors to meld.